1. Field of the Invention
The present invention relates to a real-time communications system of high communications quality and a media terminal apparatus. More particularly, the present invention relates to a real-time communications system preferably applicable to voice communications based upon VoIP (Voice over Internet Protocol) technology. The present invention also relates to a media terminal apparatus treats data according to the MIDI (Musical Instrument Digital Interface) standard.
2. Description of the Background Art
A musical instrument according to the MIDI (Musical Instrument Digital Interface) standard and the like can output MIDI data. MIDI data are not of a waveform of sound itself, but are obtained by conversion of several parameters, such as pitch, length and tone, of sound into numerical data. The performance contents of an electronic musical instrument can therefore be described with considerably smaller size than that of data directly coded from waveform itself.
Utilization of the MIDI standard makes it possible to implement a lesson method of allowing a student to store MIDI data obtained from his or her performance of an electronic musical instrument in a storage medium and send the storage medium via mail or postal service to his or her instructor staying in a remote site to notify the instructor of the performance contents, based upon which the instructor can then coach the student on his or her performance.
In addition, it is possible to use an analog telephone service provided in an ordinary public switched telephone network (PSTN) to transmit sound or voice. It is therefore not necessarily impossible to use the analog telephone service to carry out lessons of karaoke, vocal music and/or instrumental performance.
Generally, the bandwidth of voice signals transmitted by an analog telephone service is limited to a very narrow bandwidth of 300-3,400 Hz. An ordinary voice transmission is possible without any trouble in the bandwidth. Because of the limited bandwidth, however, the communications quality is too low for vocal music, karaoke and musical instrumental lesson. More specifically, for voice and sound signals of vocal music, karaoke and musical instruments, the frequency components lower than 300 Hz and higher than 3,400 Hz are very important. Nevertheless, by the analog telephone service, those important components are cut out so as not to be transmitted. Many problems are thus involved in the communications in which the frequency signals outside the voice band are treated.
Further, when sending a storage medium having MIDI data stored via postal service, there is not a problem of required bandwidth, but there is non-real-time property. Therefore, it is difficult to promote communication between a trainee and an instructor and carry out music lessons effectively.